Titanium alloys may include inhomogeneities in the form of segregates or liquations, which may lead to failure of the structural part or component made of such alloys. Therefore, high load structural parts, such as compressor disks, compressor shafts, and spacing rings in turbo engines, for example, must be free of segregations or liquations. The segregations may be areas of high hardness, caused by oxygen or nitrogen enrichment. There are also, however, soft .beta.-segregations, which for example show large areas of a .beta.-alloy concentration or content.
Due to the unacceptability of segregations or liquations in high-load parts, these segregations or liquations must be indicated or made visible. This may be achieved chemically through etching, especially surface etching, in hydrofluoric acid solutions, or electrochemically through anodization in an electrolyte. In the case of chemical etching, the segregation appears light on a dark background. Anodization makes the segregation visible as a dark spot on a light blue colored background. In all methods it is the aim to achieve the maximum possible contrast. However, achieving such high contrast is not always easily possible, depending on the type of alloy and on the segregation or liquation type.
The same problem exists, for instance, in examining resistance spot welds. The metallographic dimensional examining of the resistance weld is carried out, after etching test parts or test samples, by evaluating the resulting weld nugget. Here again, the difficulty lies in achieving a sufficiently marked contrast by the etching of the test sample or test part.